She DID tell you she had it, you just didn't know that cold sores were caused by herpes type 1.
How "almost gone" was it? Was there still a scab? Was it just red skin?
Have you ever been tested for herpes? At 35, there is an EXCELLENT chance that you have it, have kissed someone who has it (including your parents or family members), or had sex with someone with either type 1 or 2.
Ask your doctor for a type specific IgG blood test to find out.
She's right, to a point - a lot of people do have it, but she also shouldn't be performing any sexual acts on someone with symptoms. (If it was just red skin, she's probably not infectious anymore. If it was a scab, it's really hard to say at 6 days how much virus would be present.) Not everyone has it - I don't. (I have type 2, but not type 1.)
Your chances? Hard to say but probably not that high. If you already have it, close to zero, depending on how "almost gone" the sore was.
Not something I'd overly worry about.